Collecting Butterfly Orchid Measurements Together

The weather has not been inviting for a wander across the fields in recent days so instead I have been trying to find patterns in data that I have collected over the years.   In addition to the study Anne and I made of the butterfly orchids on Skye, and the ongoing work on a population of greater butterfly orchids in the Chilterns, whenever I find either of the two butterfly orchids I make measurements, as far as possible trying to get a random sample.  I used to restrict these to height, bottom leaf width, and the number of flowers, but I now take a flower photo - chosen at random - to measure the labellum length and width, the subtended angle between the pollinia,  the distance between the viscidia, the length of the lateral sepal and the angle of that sepal to the horizontal.

Greater Butterfly Orchid, Bald Hill 5.6.19

Lesser Butterfly Orchid, Cae Blaen Dyffryn 15.6.19

Hybrid, Warburg 16.6.19

I put all the data together, from 22 locations together with summaries from Skye and the Chilterns.
It includes some hybrids, mainly from Gloucestershire, but there is one from Warburg.  Altogether there are 224 observations for lesser and greater and 16 for the hybrid, (excluding Skye and the Chilterns studies) though not necessarily including all parameters for each observation

The data is very variable, but as might be expected there are clear differences between lesser and greater butterfly orchids, and indeed the hybrid.  A few examples of the averages (the differences have not been subjected to any statistical tests)

Ratio of  number of flowers to height
   LBO      0.70
   GBO     0.35 to 0.53
   Hybrid  0.69

Subtended angle between the pollinia
   LBO       4 degrees
   GBO     37 degrees
   Hybrid  15 degrees


Labellum width to height
   LBO       0.30
   GBO      0.24
   Hybrid   0.26

Spur length
   LBO      20.8mm
   GBO     27.1 to 33.8mm
   Hybrid  25.3mm

Spur length is dependent on latitude, but not to the extent I expected; the further north the shorter the spur, but shading also seems to have an  impact - shaded plants have longer spurs.  Plant height is affected by shading, but also by environment and latitude.   The Chilterns woodland greater butterfly orchids are taller than average, but have fewer flowers than would be expected for their heights.   Bald Hill, an open site, part of the Aston Rowant NNR, has stunted greater butterfly orchids yet is only a few miles from the Chilterns woodland site.   

The plant with the longest spur though was a hybrid from Warburg at 40mm (pictured above), reminiscent of long spurred orchids found in Holland, but as there was only 1 plant and it did not re-emerge this year, then all I can assume that it is simply a natural variation